JPS6291886A - Magnetic brake for clock - Google Patents

Abstract

A magnetic brake for a timepiece including a seconds wheel and a fixed magnet. The wheel is fashioned from magnetic steel. The magnet is located in vicinity of the wheel periphery and radially offset with respect to the teeth thereon.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a brake device for a gear transmission mechanism of a timepiece having a second hand wheel, and more particularly to a magnetic brake device with a fixed magnet.

[Problems to be solved by the prior art and the invention] In a portable watch equipped with a second hand wheel, especially in an electronic portable watch equipped with a pulse motor, the second hand swings at the end of the pulse motor, causing the scale dial to oscillate. It is permissible to stop at other points without directly moving up the scale. This phenomenon is caused by play in the gear system. This especially occurs in portable watches in which the motor drives the seconds wheel through one or several intermediate gears. A similar behavior is also observed in mechanical watches where the second hand is positioned off-center. In order to eliminate such unsightly movements, it has already been proposed to provide a second hand brake. Typically, this type of brake uses a spring that acts on the end of the pivot. Unfortunately, however, such a device would take up space which would add to the thickness of the watch.Currently, the thickness of a watch is an important element of the watch, so this solution is no longer practical. do not have.

It has also been proposed to provide a mechanical braking effect in such a way as to increase the friction when the second wheel rotates in its bearings by placing a magnet near the shaft of the second wheel. However, this method also takes up a lot of space within the thickness of the watch.

In another example, the pivot portion of the second hand wheel is lubricated with a lubricant. Therefore, the friction between them is viscous friction, in other words, as the speed increases, the friction also increases.

From the above, even if the brake couple is increased considerably while the gear transmission is being driven, the result is that the couple required for positioning the second hand increases only slightly. Therefore, in reality, it can be said that although energy consumption is large, the effect is small.

The object of the present invention is to provide a gear transmission that generates a brake couple that ensures good positioning of the second hand, without requiring additional space in the thickness of the watch and without noticeably increasing energy consumption. brake.

[Means and effects for solving the problem] The above object is to make the second hand wheel from magnetic steel, and to set a position near the periphery of the second hand wheel that is offset in the radial direction with respect to the teeth of the second hand wheel. This can be achieved by placing a magnet at

By arranging magnets around the periphery of a gear wheel made of magnetic steel, it is possible to achieve a particularly efficient brake for positioning the gear wheel, a surprising method that consumes little energy at the same time. determined effectively.

Until now, those skilled in the art have endeavored to use magnetic materials that are as soft as possible, ie, have a low magnetic coercive field. In addition, the magnets were placed as close to the center as possible to make the attraction force as strong as possible and generate a friction couple.

It is conceivable that in the arrangement according to the invention the braking action takes place because the steel of the gear in the vicinity of the magnet moves through a complete hysteresis cycle with each gear change. It is known that the coercive magnetic field of steel is larger than that of soft iron. This brake couple appears to be generated inter alia in this way by this magnetic phenomenon.

This phenomenon hardly changes with speed. This results in the fact that a steel seconds wheel consumes less energy than one made of soft iron to achieve the same positioning effect.

On the other hand, steel fabrication has many advantages over soft iron fabrication from a manufacturing point of view.

Soft iron is difficult to machine, easily curls, and deforms with the slightest impact, making it unsuitable for use with teeth p[. Steel, on the other hand, is easier to machine and is more impact resistant, especially when hardened.

〔Example〕

The drawing shows a base plate 10, a bridge 12, and a second hand wheel 14 which is pivotally supported on the bridge 12 and the base plate 10.

More specifically, a hole is formed in the plate 10, and a tube 16 is fitted into the hole.

A hole is also formed in the bridge 12, into which a jewel 18 is set, which jewel has a hole therein which is coaxial with the tube 16. The tube 16 and the jewel 18 constitute a bearing portion of the second hand wheel 14. The bridge 12 further has a hole at a distance from the jewel 1, into which a magnet 20 magnetized in the axial direction is fixed. The thickness of the magnet 20 is substantially the same as the thickness of the bridge 12. The magnet 20 is cylindrical and has a diameter that is substantially equal to the hole in the bridge 12 and is adapted to be press fit and snugly fitted therein. The shirts 1 to 22 are attached to the second hand wheel 14, forming a solid disk portion 24. A steel pinion is attached to the shaft 22 similarly to the disk portion 24 .

The disk portion 24 is press-molded and riveted to the shaft 22. A toothed portion 26 is formed at the periphery of the disc portion 24 . The distance between the axis of the second hand 4 and the axis of the magnet 20 is such that the magnet 20 is close to the periphery of the second hand wheel 14 but is offset in the radial direction with respect to the teeth 26 of the second hand wheel 14. It is set to be placed.

For clock operations where the second hand shows signs of poor positioning,
Various attempts were made. This defect is caused by play in the gearing and is caused by bounce of the gear transmission at the end of the motor pulse. In order to eliminate this defect, the second hand wheel was made of steel and a magnet was pushed into the hole in the bridge.
I converted the above movement. To be more precise, the second hand wheel with a diameter of 2.2 mm (heavy electric) and a height of 0.10 mm (1 min) is made of hard steel sand-like (Sandw).
ik) 14 P (Vickers hardness, 530+1ν
) is formed.

This type of material has a coercive field substantially equal to 50 Oe and a residual magnetic induction of 9000 Gauss (Oe) in the periphery.
I have G). The magnet has a diameter of 0.30 mm.
A piece of platinum cobalt with a length of 0.50 mm is press-fitted into the bridge, and the distance between the axis of the second hand wheel and the axis of the hole is 0.5 mm.
It is 82 mm. The distance 'm (gap) between the magnet and the second hand wheel is equal to 0.12 mm.

A brass second hand wheel was prepared and comparative measurements were made without the above movement conversion. In this case, the pair of brake devices consists of a 0.03 mm thin metal piece bent into the shape of a spring and inserted between the seconds wheel and the dial. This measurement result shows that the variation in the position of the second hand wheel was reduced by the three factors related to the movement of the magnetic brake described above.

On the other hand, changes in other factors such as consumption, effective couple, or functional limitations have not been confirmed as effective forms. In no case do they amount to more than a few percent.

Other types of steel can also be used for this seconds wheel section. In order to obtain valid results at the same time, the holding field must be 1
0 oersted (Oe) to 100 oersted (Oe)
) is desirable. If the magnetic field is too strong or too weak, the brake couple will be reduced.

On the other hand, if it is too strong, the magnet will no longer operate in a complete hysteresis cycle.

Depending on this situation, different types of magnetic materials have to be selected. Generally speaking, anisotropic ferrite,
Materials with high coercive fields such as platinum cobalt and rare earth based materials are most suitable.

In all cases, the magnet and the second hand wheel, and the distance separating them, must be chosen such that the steel aligned with the magnet is close to saturation.

In actual trials, we found that the thickness of a cylindrical magnet is approximately twice its diameter, and that the thickness of a second hand wheel is approximately equal to the gap, and that this gap is 3 to 3 times the length of the magnet. It is less than 6 times wider.

Such a dimensional relationship is applicable even when the magnet is made of platinum cobalt. If other materials are used, this dimensional relationship must be modified by the properties of the material and, in particular, by its coercive field and remanent induction. More precisely, this length and diameter must decrease with increasing coercive field and remanent induction, respectively.

In the case of small portable watches, platinum-cobalt is particularly popular despite its high price. This has the advantage of not being sintered. In other words, it has very high mechanical resistance and good machinability, so
There is no risk of breakage when press-fitting the magnet.

A few tricks have been made for the recommendation of portable watches; it is clear that the solution described above is equally valid for many watches.

[Brief explanation of drawings]

The figure is a sectional view showing a brake device according to the present invention together with a partial view of a portable watch. 10... Base plate, 12... Bridge,
14...Second hand wheel, 16...Tube, 18."
- Jewelry, 20... Magnet, 22... Shaft, 24... Disc part, 26... Gear.

Claims (1)

[Claims] 1. In a magnetic brake using a fixed magnet for a gear transmission device of a timepiece including a second hand wheel, the second hand wheel is formed of magnetic steel, and the magnet is attached to a peripheral portion of the second hand wheel. A magnetic brake for a timepiece, which is disposed near the second hand wheel and offset in the radial direction with respect to the teeth of the second hand wheel. 2. The magnetic brake for a timepiece according to claim 1, wherein the magnet is made of a highly magnetic material having a highly coercive magnetic field. 3. The magnetic brake for a timepiece according to claim 2, wherein the magnet is made of platinum cobalt. 4. The magnetic brake for a timepiece according to claim 1, wherein the second hand wheel is made of hard steel. 4. The magnet has a cylindrical shape, the diameter thereof is approximately half the length of the cylinder, the dimension of the gap between the magnet and the second hand wheel is equal to the thickness dimension of the second hand wheel, and The magnetic brake for a timepiece according to claim 1, which has a length of one-third to one-sixth of the length of the magnet.